Method and apparatus for controlling a jet pump



July 22, 1969 R. GsLlNG 3,456,871

METHOD ANI) APPARATUS FOR CONTROLLING A JET PUMP Filed July 18, 1967 2Sheets-Sheet 1 :wc/WA Vf 0 fr v p FIG. la.:

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July 22, 1969 R. GsLlNG 3,456,871

METHOD AND APPARATUS FOR CONTROLLING A JT PUMP Filed July 1a, 1967 "2sheets-sheet z n t L h m i# a@ .EQg Eg g t Q t q g s n i i rif I m mi in l Q mi N Q *N Q 1 N N Q e u Ril i Q INVENTORI Ll. o ROLF GdsLaNGUnited States Patent O 3,456,871 METHOD AND APPARATUS FOR CONTROLLING AJET PUMP Rolf Gsling, Hannover, Germany, assignor to Schutte andKoerting Company, Cornwells Heights, Pa., a corporation of PennsylvaniaFiled July 18, 1967, Ser. No. 654,190 Int. Cl. F04f 5/48; F02k 11/00ABSTRACT F THE DISCLOSURE U.S. Cl. 230--111 4 Claims A control systemfor a jet pump, such as a stream jet vacuum pump wherein the thrust andsuction streams initially flow at supersonic speed, in which theposition of the shock zone or transition surface between the supersonicand s'ubsonic velocities -of the flow of thrust and suction streams 'inthe diffuser is used to control the rate of flow of the thrust medium.

This invention relates to a method and apparatus to adjust or control ajet pump of the type having a compressible flow in the diffuser and asupercritical ratio of suction to discharge pressures.

In a jet pump of this type, the vmixture of the motive or thrust stream,which in most instances will be steam, and the suction stream flowsinitially at a supersonic velo-city. The change from supersonic tosubsonic velocity of the thrust and suction stream Will `occur in ashock zone. This shock zone will 'be displaced in a direction toward thethrust nozzle when the reaction or back pressure increases or when thethrust pressure or thrust fiow decreases. Once this shock zone movesinto the intake .Y

cone of the diffuser, the jet pump becomes unstable in operation and thepumping action can fail completely. In a similar manner when thereaction or back pressure decreases or thrust flow increases, the shockzone will be displaced into the exit cone of the diffuser. With theshock zone in the exit cone of the diffuser, the -rate of ow of themixture of thrust and suction streams is accelerated increasing thepressure drop across the diffuser and decreasing the efficiency of thejet pump. The lowest ratio of flow of thrust fluid to flow of thesuction field is attained when the jet pump is just about in stableoperation which is when the shock zone is in the throat of the diffuseror just at the beginning of the diffuser outlet cone.

In daily actual operation of jet pumps of this type, variations in backpressureV as well as variations in the pressure of the thrust stream dooccur. Prior to the present invention, to avoid such a jet pump fromreaching an unstable operation the jet pump was operated with an excessamount of thrust stream flow to take care of the maximum back pressurewhich could occur and the minimum thrust stream pressure which couldoccur. VConsequently, it will be seen that prior to the presentinvention, jet pumps of this type operated most of the time with anexcessive use of thrust fluid. l

With the foregoing in mind, a primary object of the present invention isto provide means for controlling or regulating a jet pump of this typeto permit the shock zone to remain in the optimum performance positionregardless of fluctuations of back pressure or thrust stream pressure.This is accomplished in the present invention by using a measurement ofa condition of the stream of thrust and suction fluids within the throatof the diffuser as a means for regulating the -rate of flow of thethrust stream to maintain the shock zone in the throat of the diffuser.The condition of the stream of thrust and suction fluids in the diffuserused to control the rate of flow of the thrust stream fluid can be ameasurement of the "ice static pressure gradient along the diffuser, thevelocity gradient along the diffuser or a temperature gradient along thediffuser.

The various features and details of the present invention will be morefully described with reference to the accompanying drawings in which:

FIG. l is a schematic illustration of the thrust stream nozzle anddiffuser of a jet pump with static pressure taps spaced along thediffuser in an area adjacent the throat of the diffuser;

FIG. la is a graph showing the static pressure along the diffuser axiswith the shock zone at designated points in the diffuser;

FIG. 2 is a schematic illustration of the thrust stream nozzle anddiffuser of a jet pump with a series of pitot tube pressure taps formeasuring the velocity of flow at predetermined points along thediffuser;v

FIG. 2a is a chart showing the relationship of the pitot tube pressurealong the diffuser axis with the shock zone at designated locationswithin the diffuser; and

FIG. 3 is a schematic diagram of a jet pump together with a controlsystem for controlling the jet pump in accordance with the method lofthe present invention.

The jet pump to which the present invention is applied comprises aconventional nozzle 10 including an adjustable spindle 11 to controltheflow of the thrust medium and a diffuser 12 having an inlet cone 13,a throat portion 14 and an outlet cone .15. A reversible motor 16 isprovided to move the spindle back and forth relative to the thrustnozzle 10 to c-ontrol the rate of flow of the thrust medium. Stream orother thrust medium will ibe supplied to the jet pump through an inletpipe 17 leading to the nozzle 10. A conduit 18 leading into a chamber 19surrounding the thrust nozzle 10 is connected to the source (not shown)of the suction stream. The exit of the outlet cone of the diffuser maybe connected to the condensation and gas separating tank 20 in which thethrust fluid is separated from the suction fluid.

Referring specifically to FIGS. 1 and la, there is shown the staticpressure along the diffuser when the shock wave or transition zonebetween supersonic and subsonic flow of the mixture of thrust andsuction mediums is at points A through G, respectively. In addition, inFIG. 1 there are static pressure taps P1, P2, P3, and P4 as shown in thethroat of the diffuser and the inlet end of the outlet cone.

It will be seen from FIG. la that the static pressure is substantiallyconstant throughout the length of the throat of the diffuser to theshock wave at which point the static pressure increases abruptly. Also,as shown in FIG. la, the static pressure will decrease in the outletcone of the diffuser from `the exit of the throat of the diffuser to thepoint where the shock wave exists at which time the static pressure willabruptly increase and thereafter increase substantially uniformlythroughout the length of the outlet cone.

Thus, for example, if it is desired to maintain the shock wave atposition C which is directly at the pressure static tap P2, the pressureat the pressure static tap will be as shown at P20 in FIG. la. If theback pressure irlcreases or the pressure of the thrust fluid decreases,Vthe shock wave will be moved to the left with respect to P2 and thepressure at P2 will abruptly increase. Similarly, if the back pressurewould decrease or the thrust pressure increase, the shock wave will `bemoved to the right with respect to P2 and the pressure at P2 willabruptly decrease. Accordingly, by maintaining the pressureat P2constantjand maintaining this pressure as shown at P2C, the shock wave-Will be maintained at position C.

Similarly, the static pressure gradient at thev outlet of the throat andinlet end of the outlet cone of the diffuser may be used to control theposition of the shock wave when it is desired to maintain the shock wavein an optimum position between two static pressure taps. It is evident,for example, if the shock waves were at position D, the pressuredifferential between P2 and P3 would be as shown at points P212 and P3Din the chart of FIG. la. Should the shock wave move forwardly in theoutlet cone, for example, to E, the pressure differential between P2 andP3 would change to that as shown at P2E and P31.; in FIG. 1a. Thefollowing table shows the pressure gradient measured at three points-P1,P2, and P3 in FIG. 1 as the shock wave moves through positions A, B, Dand G.

Shock zone position: Pressure gradient Should it be desired to maintainthe shock wave at position D, it can be seen that the flow of thrustmedium must be increased when P1 is greater than P2 but must be reducedwhen P2 is less than P3 until the condition in which P1 is greater thanP2 which in turn less than P3 is obtained. If it is desired to use fourmeasuring Points P1, P2, P3, land P1 the pressure gradients betweenthese measuring points for shock wave positions at A, B, D, F, and G areas follows:

Again, a desired condition for regulating flow of thrust medium is whenthe shock wave is at point D utilizing these above points. When theshock wave is at position D, P1 is greater than P2 and P3 is less thanP1. When P1 becomes less than P2 the ow of thrust medium must beincreased and when P3 becomes greater than P1 the flow of thrust mediummust be decreased.

FIG. 3 illustrates schematically a control system for carrying out themethod of the present invention. `In the system of FIG. 3 there arethree static pressure taps 21, 22 and 23 which correspond to thepressure taps P1, P2 and P3 described above. Also in this system, it isdesired to maintain the shock wave at position D which corresponds tothe position D of FIG. 1.

In the control system of FIG. 3, the static pressure taps 21, 22 and 23are connected to two similar pressureresponsive switches 24 and 25. Theposition of the switches 24 and 25 is controlled by spring biaseddiaphragms 26 and 27, respectively. With equal pressure on both sides ofthe diaphragm, the switches 24 and 25 are in the position as shown inFIG. 3 with a circuit completed through the contacts 24a and 25a,respectively, of the switches. A conduit 28 connects the pressure tap 21with one side of the diaphragm 26 of the switch 24 and a conduit 29connects the pressure tap 23 with one side of the diaphragm 27 of theswitch 25. A common conduit 30 connects the pressure tap 22 with theother sides of the diaphragms 26 and 27.

In operation as the jet pump of the present invention is initiallyturned on, the spindle 11 will be in its fully retracted positionpermitting the maximum flow of motive stream through the nozzle 10. Inany position of the shock wave within the inlet cone 13 or in the throat14 of the diffuser upstream of the pressure tap 22, the pressure at thetap 21 will be less than the pressure .at the tap 22 which in turn willbe less than the pressure at the tap 23. With this pressure relationshipbetween the taps 21, 22 and 23, the switch 24 will be in the position asshown in FIG. 3 with a circuit completed through the contact 24a and theswitch 25 will be in a position with the circuit completed through thecontact 25b. With the switches in this position, `a circuit is completedthrough the switch 24 to the contact R of the motor 16 causing the motor16 to retract the spindle 11. As the shock wave moves past the pressuretap 22, for example, to the position shown in D in FIG. 3, the pressureat the tap 21 is greater than the pressure at the tap 22 which in turnis less than the pressure at tap 23. With this pressure relationshipexisting, the switch 24 will be in a position wherein the circuit iscompleted through contact 24b and the switch 25 will be in a positionwherein the circuit is completed through contact 25b. With the switchesin these positions, no circuit will be completed to the motor 16 andthus, the spindle will remain in the position it is in when the shockwave reaches position D. Should the shock wave move into the outlet cone15 of the diffuser to a position downstream of the pressure tap 23, thepressure at the tap 21 will be greater than the pressure at tap 22 whichin turn will be greater than the pressure at tap 23. With this pressurerelationship existing, the switch 24 will be in a position in whichcircuit is completed through the Contact 24b and the switch 25 will bein a position wherein the circuit is completed through the contact 25a.With the switches 24 and 25 in this position, a circuit is completedthrough the switches 214 and 25 to the contact F of the motor 16 whichcauses the motor to drive the spindle 11 forward throttling the motivestream passing through the nozzle 10 'and decreasing the rate of flow ofthe motive stream. Decreasing the rate of flow of the motive stream willcause the shock wave to move in a direction upstream of the diffuseruntil the shock wave reaches the previously defined position D' betweenthe pressure taps 22, and 23 at which time operation of the motor 16will halt. Thus, it will be seen that this control system of FIG. 3 willcause the shock wave to assume a position at D and maintain the shockwave at this position. Should conditions within the system be such as tocause the shock wave to move away from this position, the control systemwill compensate for these conditions and move the shock wave back to theposition D'.

Referring now to FIGS. 2 and 2a, there is shown the pitot tube pressurealong the diffuser when the shock wave or transition zone betweensupersonic and subsonic ow of the mixture of thrust and suction mediumsis at points A through G respectively. In addition, in FIG. 2 there arepitot tubes P11, P12, P13, and P11 as shown in the inlet end of theoutlet cone of the diffuser.

It will be seen from FIG. 2a that the pitot tube pressure issubstantially constant throughout the throat of the diffuser and issubstantially constant downstream of the shock wave in the outlet cone.However, the pitot tube pressure drops uniformly from the inlet end ofthe outlet cone to the position of the shock wave. It is evident, forexample, if the shock waves were at position B, the pressure at P11would be greater than the pressure at P12 as shown at P1113 and P1213 inFIG. 2a and that the pressure at P13 and P11 rwill be the same as thepressure at P12. Also, if the shock wave were at position D, thepressure at P12 will be as shown in P1213 in FIG. 2a which will be lessthan the pressure at P11 but greater than the pressure at P13.

The following table shows the pressure gradient for three points ofmeasurements Pn, P12, and P13 as the shock wave moves through positionsA, B, D and G.

Shock wave zone: Pressure progress The shock wave position at B is theoptimum position and it can be seen that P11 is greater than P12 andthat when P12 is equal to P13, the shock wave s at the point B. If P11becomes equal to P12 the volume of the motive stream must be increased.Similarly, if P12 becomes greater than P13, the volume of the motivestream must be decreased. Thus, this pressure differential may be usedto provide a control signal to control the flow of the motive stream. Ifit is desired to use four measuring points Pn, P12, P13, and PPPM thepressure gradients between these measuring points for shock wavepositions A, B, D. F and G are as follows:

With four measuring points, it will be possible to maintain the shockwave positions between B and D. For example, when Pu becomes equal toPiz the flow of motive stream must be increased and when P13 becomesgreater than P14 the flow of motive stream must be reduced.

Only one example has been given of a control system utilizing pressuredifferentials or pressure gradient throughout the diffuser to controlthe position of the shock wave. However, it can be Seen that when usingstatic pressure taps or pitot tube taps, there are pressure gradients inthe diffuser which can be used to provide a control signal to controlthe ow of motive stream which in turn will control the position of theshock zone within the diffuser.

While particular embdiments of the present invention have beenillustrated and described herein, it is not intended to limit theinvention to such a disclosure and changes and modifications may beincororated and embodied therein within the scope of the followingclaims.

I claim:

1. In a control system for a jet pump in which the stream of motivefluid and suction Huid initially flows at a supersonic velocity and isconverted at a shock wave within said jet pump to sonic velocity; saidjet pump having a diffuser including a central throat portion, an inletcone converging inwardly toward the central throat, an outlet conediverging outwardly away from the central throat, an inlet to said inletcone in fluid communication with said suction medium, an adjustablenozzle adjacent the inlet to said inlet cone for supplying said thrustmedium, and adjusting means for said nozzle to control the ow of saidthrust medium; -a plurality of pressure taps spaced longitudinally ofsaid diffuser to measure pressure at preselected points spacedlongitudinally of said diffuser, one of said pressure taps positioned tomeasure pressure in said throat at one of said preselected pointsclosely adjacent said outlet cone, and at least two of said pressuretaps positioned in longitudinally spaced relation in said outlet conewith the first of said two pressure taps spaced a preselected distancefrom said throat to measure pressure at a first preselected point insaid outlet cone and the second of said two pressure taps spaced fromsaid throat further than said preselected distance to measure pressureat a second preselected point in said outlet cone; and control meansoperatively connected to said adjusting means for said nozzle, saidcontrol means responsive to the pressure measured `by said plurality ofpressure taps to adjust said nozzle to maintain the transition shockwave between supersonic and sonic velocity of said stream of motive andsuction fluids between said one preselected point in said throat andsaid second preselected point in said outlet cone.

2. A control system in accordance with claim 1 in which said controlmeans operates to open said nozzle to increase the ow of thrust tluidwhen said shock wave is between said nozzle and said first preselectedpoint in said outlet cone and operates to close said nozzle when saidshock wave is beyond said second preselected point in said outlet conein a direction away from said rst shock wave between said first andsecond preselected points in said outlet cone.

3. A control system for a jet pump in accordance with claim 2 whereinsaid pressure taps are static pressure taps.

4. A control system for a jet pump in accordance with claim 2 whereinsaid pressure taps are pitot tube pressure taps.

References Cited UNITED STATES PATENTS 2,140,306 12/ 1938 Beals 230-100X 2,968,147 1/1961 Truly et al.

2,996,878 8/1961 Leeper 137-15.2

3,029,601 4/1962 Arnberg et al.

3,030,768 4/1962 Yahnke IS7-15.2

3,065,599 11/ 1962 Dew.

3,086,357 4/1963 Rubin et al. 137--15.2

3,102,387 9/1963 Caspar et al.

3,149,474 9/1964 Goodman 230-111 X 3,172,622 3/1965 Kalika et al.137-152 X FOREIGN PATENTS 1,057,828 10/ 1959 Germany.

1,157,851 5/1964 Germany.

DONLEY I. STOCKING, Primary Examiner WARREN I. KRAUSS, AssistantExaminer U.S. Cl. X.R. 137-152, 271

P04050 (fu/69) Patent No.

lnventor(s) Dated Jul) 22, 1969 Rolf Gosling It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

Column l, line 14,

Column 5, line (SEAL) Attest:

Edward M. Fletcher, Ir.

Altestng Office-f 1, line 45,

